1. 轮询全局变量

2. 使用事件驱动

A. 信号量

(1) 二进制信号量（resource/binary semaphore）< 互斥锁 Mutex( Mutual exclusion ) >

信号量只有二进制的0或1

OS_Use() Claims a resource and blocks it for other tasks

OS_Unuse() Releases a semaphore currently in use by a task.

OS_Request()  Requests a specified semaphore, blocks it for other tasks if it is available. Continues execution in any case.

Claims a resource and blocks it for other tasks.

Requests a specified semaphore and blocks it for other tasks if it is available.

Continues execution in any case

 

 

(2) 计数信号量（counting/general semaphore）

信号量是一个任意的整数

OS_SignalCSema() Increments the counter of a semaphore

OS_WaitCSema() Decrements the counter of a semaphore.

OS_CSemaRequest() Decrements the counter of a semaphore, if available.

B. 消息

(1) 邮箱 - 1..127 字节的消息 ( 消息字节数 -- 固定的)

OS_PutMail() Stores a new message of a predefined size in a mailbox.

OS_WaitMail() Waits until a mail is available, but does not retrieve the message from the mailbox.

OS_GetMail() Retrieves a message of a predefined size from a mailbox.

OS_PeekMail() Reads a mail from a mailbox without removing it

(2) 队列 - 大于 127 字节的消息 ( 消息字节数 -- 可变的 )

OS_Q_Put() Stores a new message of given size in a queue.

OS_Q_PutBlocked() Stores a new message of given size in a queue. Blocks the calling task when queue is full.

OS_Q_GetPtr() Retrieves a message from a queue.

OS_Q_GetPtrCond() Retrieves a message from a queue, if one message is available or returns without suspension.

OS_Q_GetPtrTimed() Retrieves a message from a queue within a specified time, if one message is available.

OS_Q_Purge() Deletes the last retrieved message in a queue.

C. 事件

(1) 任务事件 - 每一个任务有 1 字节 事件掩码 ( 8 个事件 )

OS_SignalEvent() Signals event(s) to a specified task.

OS_WaitEvent() Waits for one of the events specified in the bitmask and clears the event memory after an event occurs.

OS_WaitSingleEvent() Waits for one of the events specified as bitmask and clears only that event after it occurs.

OS_WaitEvent_Timed() Waits for the specified events for a given time, and clears the event memory after an event occurs.

OS_WaitSingleEventTimed() Waits for the specified events for a given time; after an event occurs, only that event is cleared.

(2) 事件对象 - the signaling function does not need to know which task is waiting for the event to occur

OS_EVENT_Wait() Waits for an event. 

OS_EVENT_WaitTimed() Waits for an event with timeout and resets the event after it occurs. 

OS_EVENT_Set() Sets the events, or resumes waiting tasks. 

OS_EVENT_Reset() Resets the event to none-signaled state.

OS_EVENT_Pulse() Sets the event, resumes waiting tasks, if any,and then resets the event.

OS_EVENT_Get() Returns the state of an event object.